1. Field of Invention
The present invention relates to a device for the governing of the supercharging pressure of a turbocharger fed internal combustion engine, wherein the same pressure is controlled by a feedback system as a function of preselected engine parameters.
The trend in the internal combustion engines is presently towards increasing compression ratios to the purpose of improving the thermodynamic efficiency and reducing the fuel consumption, e.g., by resorting to the turbochargers.
But increasing the supercharging pressure beyond certain limits is not possible, because of the tendency of the engine to knock, especially if the fuel is not endowed with high antiknocking characteristics, as well as in order to prevent the turbocharger from exceeding the maximum allowable revolution speeds.
Consequently, valves are used which are able to exhaust a portion of the supercharging air fed by the turbocharger, or valves able to divert from the turbines a portion of the exhaust gases of the engine.
Generally then, in the presence of knocking, the spark advance is adjusted, by delaying it, to the purpose of allowing the engine to operate under conditions far from the operating conditions which favour the phenomenon.
2. The Related Art
Devices for the governing of supercharging pressure of internal combustion engines are well known; both open-loop and closed-loop types thereof are currently available.
The devices of the second type are more complex, but surely much more advantageous, in as much as they allow the supercharging pressure to be optimized through a monitoring of the actual operating conditions of the engine; to the contrary, the devices of the first type oblige the designers to adopt a fixed limit value, determined by the most unfavourable operating conditions.
Also governor devices of the closed-loop type are known, which are accomplished by programmed microcomputers which are able to compute, as a function of selected engine parameters, the values of physical quantity of actuation, as well as the values of the physical quantity for feedback-control, to the purpose of verifying whether the actual value of the supercharging pressure or of a quantity correlated to it, corresponds to the control value.
The values of the above quantities are experimentally found under the different engine operating conditions, and are those which show a determined margin of safety relatively to the values which cause a combustion with knocking, with the spark advances being optimized relatively to the same phenomenon and for fuels of determined qualities.
These values are memorized in the permanent memory of the microcomputer as a function of the engine parameters preselected for defining the operating conditions of the same engine.
It has been found that these devices operate efficaciously when the engines operate with an ambient temperature higher than determined values generally higher than of ambient air under standard conditions.
To the contrary, for lower temperatures a certain undesired penalization was found to detriment of the power supplied by the engine because, due to the low temperatures of intaken air and of the consequent lower temperatures of compression end, also the pressure inside the combustion chamber assumes values having wider margins relatively to those which involve the knocking.